Pre-order · ships on 10 November 2026

Your JK BMS, without walking into Bluetooth range

The JK app is great until you are on the other side of the house. MoniWatt for JK BMS reads the BMS over its RS485 port and puts the cells, the balancer and the alarms on your home Wi-Fi.

Pre-order now — €49.00 See what it shows →

Colour screen + Wi-Fi dashboard
No subscription
14-day returns, 2-year legal guarantee

MoniWatt for JK BMS Wi-Fi box with screen showing pack charge, voltage and current

< 0.5 Wpowered by USB-C

0settings written to your battery

€49.00screen and cables included

10 Novpre-orders ship

JK boards became the default choice for DIY home batteries for good reasons: a strong active balancer, accurate cell measurement, and on the inverter series, proper RS485 and CAN ports to talk to the inverter. Yet most owners still check their pack through Bluetooth, standing next to the cabinet with the app open.

MoniWatt for JK BMS stays connected to the BMS’s RS485 port all the time. It reads each cell, the balancer activity and the temperatures, keeps the curves of the day, sends an e-mail when something trips, and makes all of it available in Home Assistant. No Bluetooth range problem, no phone that must stay in the garage, and nothing written to your BMS settings.

What you get

Every cell, live

All cell voltages with min, max and delta, refreshed every few seconds.

The balancer at work

See balancing current and which cells it is moving charge between.

Temperatures and MOS

Pack probes and the power MOSFET temperature, logged through the day.

Alarms you will not miss

Cell over- or under-voltage, over-current, temperature and wire resistance warnings, by e-mail.

Home Assistant without ESPHome

Plug in, enter your MQTT broker, done. No soldering an RS485 board onto a dev kit.

Read-only

Your protection parameters stay exactly as you set them in the JK app.

A day in the life of your pack

The dashboard keeps a full day of charge, discharge and state of charge, and alongside it the cell delta. Watch it widen as the pack approaches full, then close as the active balancer catches up. If it no longer closes, it is time to look at that cell.

Turn on the optional history to keep three years of data, compare seasons and export CSV for your own analysis.

Live dashboardLive

SOC82%

Power-416W

Cell Δ12mV

ChargeDischargeState of charge

Up and running in three steps

PlugThe supplied cable goes into the RS485 port of your JK BMS battery; USB-C into any phone charger.
ConnectJoin the box’s Wi-Fi from your phone, pick your home network and set a password. No app to install.
WatchOpen the dashboard in any browser, add it to Home Assistant, and set your alerts.

Full installation guide →

Made for JK BMS

Models	JK inverter BMS (RS485 / CAN boards)
Connection	RS485 port, RJ45 cable included
Your existing wiring	Untouched — the box reads, it never writes
Network	Your home Wi-Fi (2.4 GHz)
Integrations	Home Assistant
Power	USB-C, under 0.5 W

Another JK BMS model? Tell us when you order: your box is prepared and tested for it.

RS485 RJ45 socket and USB-C power socket of MoniWatt for JK BMS

Your data, your way

The values the box reads can go into Home Assistant, where you build your own dashboards and automations. Here is what a reading looks like.

Home Assistant guide →

GET http://moniwatt.local/api.json

{
  "soc": 91, "voltage": 54.42, "current": 6.1,
  "cells": [3.402, 3.401, 3.405, 3.398, ...],
  "delta_mv": 7, "balancing": true, "balance_current": 0.6,
  "mos_temp": 31.0, "temps": [22.4, 22.9], "cycles": 87
}

Plugs into the RS485 port

JK inverter BMS boards have RJ45 communication sockets for RS485 and CAN. The box connects to an RS485 socket with the supplied cable and is powered by USB-C. 70 × 70 × 36 mm, with a colour screen showing the essentials.

It shares its design with Pylon-Monitor, already monitoring Pylontech batteries across Europe, and uses our RS485 / CAN board with firmware written for the JK protocol.

Designed and assembled in France

Each box is prepared and tested in France before it ships, by the team that makes Pylon-Monitor for Pylontech owners.

Questions before buying? Write to [email protected]: a person answers.

MoniWatt for JK BMS

€49.00

VAT not applicable (art. 293 B CGI) · shipping calculated at checkout

MoniWatt for JK BMS with colour screen and RS485 / CAN interface
RJ45 cable for the JK RS485 socket
USB-C cable

Pre-order now

Ships on 10 November 2026 · free cancellation until dispatch

Questions people ask first

Which JK boards work with it?

We target the JK inverter BMS series, the boards with RJ45 RS485 and CAN sockets designed for 48 V home storage. The older Bluetooth-only active-balancer boards have no RS485 port on RJ45 and are not the focus. Tell us your board model when you order.

Do I still need the JK app?

To change settings, yes. To watch the pack, no: the box covers that, over Wi-Fi.

Can it read several JK boards?

That is part of our validation for paralleled packs on one RS485 line, each with its own address. Give us your board count.

Will it interfere with my inverter?

It is read-only and uses a free RS485 socket. If your inverter itself communicates over RS485 on a shared line, tell us its model before shipping.

All questions →

Stop carrying your phone to the BMS Bluetooth range

Order MoniWatt for JK BMS and read your pack over Wi-Fi from anywhere in the house.

Pre-order for €49.00Ships on 10 November 2026 · free cancellation until dispatch